The goals of this project are to 1) investigate the mechanisms by which inducible changes in the visual pigments of fishes are brought about, and 2) to understand how these changes are adaptive. The effects of light and temperature will be studied, with emphasis placed on the mechanisms by which these environmental factors change the visual pigments. The role of hormones, particularly thyroxine, in control of carotenoid balance of the pigment epithelium of the eye will be investigated. In turn, the conditions of light and temperature which affect incorporation of the carotenoids (Vitamin A1 and A2) into visual pigment will be monitored before and after experimental treatments by computer-assisted spectroscopy of retinal extracts. The consequences of changes in the visual pigments will be monitored in terms of their effects on visual sensitivity, which will be determined by measuring electrical activity in the optic tectum of fish exposed to varied hues of light. Significant alterations in visual spectral sensitivity will be related to visual behavior in the photic conditions of the natural habitat. The inheritance of opsins and paired pigment systems in unique stocks of poeciliid and goodeid fishes will be studied by selective crossing of intra-fertile species. By developing a system for analysis of phenotypes, I will be able to learn more about the evolution of visual pigments.